1. Field of the Invention
This invention relates to electronic systems for disabling the operation of machinery when an object is detected in a danger area and more particularly to photo-electric systems of this type.
2. Background of the Invention
A variety of systems exist for detecting the presence of a foreign object in the area of moving parts in machinery in general and in presses, saws, molding machines, etc., in particular, in order to prevent the operator or others in the proximity from being harmed by the operation of the machinery. Photodetectors are often used to sense an obstruction in a light path to trigger the power disconnect apparatus in these safety devices; however, devices that only sense obstruction along a line path have proven inadequate for safety purposes and good practice as well as government regulations require that dangerous machines be equipped with safety devices to disable the machine when a foreign object is inserted into the danger area from any direction. Systems have therefore been developed which provide curtains of light to guard the danger area. An object inserted into the curtain at any point will trigger the disabling of the operating machine.
These light curtains have typically employed a plurality of photodetectors, each sensing a different one of a series of light beams disposed parallel to one another so as to define a plane. The high cost of this approach had led to efforts to use a single photodetector, or other radiation detector, to protect a large area by reflecting a single beam along a zig-zag path or by using a rotating mirror to cause a single beam to reciprocate along the protected path. The present invention provides a light curtain system of the type employing a single photodetector which is unique in configuration so as to be relatively simple in construction and reliable in operation.